This invention relates to improvements in the purification of aluminum and more particularly to improvement in the fractional crystallization process for the purification of aluminum.
Because of the growing awareness of the limitations of natural resources, particularly energy resources, considerable effort has been expended to produce alternate sources. One such source which is considered to have exceptional potential to fulfill this need is the energy from a fusion nuclear reactor. However, because of the need to isolate or confine the radioactive media involved, considerable investigation is underway to develop materials for the reactor which will not subsequently present disposal problems. For example, if a high purity aluminum were used in the reactor, the radioactivity of such materials would be reduced by a factor which, depending upon the extent of the purity of aluminum, could be as much as a million a few weeks after shutdown. By comparison, if stainless steel were used for the same application, this reduction would take about 1000 years, obviously presenting difficult problems in disposing of such materials.
The use of high purity and extreme purity aluminum is also of growing interest in the stabilization of superconductors. In this application, the electrical energy is transferred at cryogenic temperatures, e.g. 4.degree. K, where the electrical resistance is very low. The higher the purity of the aluminum metal, the lower its resistance, i.e. the higher its conductivity at such low temperatures.
One method used in the prior art for the purification of aluminum is referred to as preferential or fractional crystallization. Such crystallization methods are disclosed by Jarrett et al in U.S. Pat. No. 3,211,547 and by Jacobs in U.S. Pat. No. 3,301,019, incorporated herein by reference. These patents involve the removal of heat from the surface of molten aluminum thereby forming higher purity aluminum crystals in the impure molten aluminum. The pure solid crystals of aluminum are then tamped and packed into the bottom of the crystallization apparatus. The impure molten aluminum is then drained from the apparatus followed by remelting of the pure aluminum which may then be withdrawn in one or several fractions of differing purity depending upon their dilution with impure molten aluminum contained between the crystals prior to remelting.
It is an object of this invention to provide improvements in the purification of aluminum by the fractional crystallization process. This and other objects of the invention will be evident from the specification and drawings.